The lava dome producing eruption at Cleveland volcano, first observed on July 29, is continuing. AVO has received no new observations or information about activity at the summit since August 2 and the last thermal anomaly observed was this morning. Earlier this week, AVO raised the Aviation Color Code to Orange and the Alert level to Watch in response to observations made on July 29 that an effusive eruption had produced a small, dome-shaped accumulation of lava in the summit crater of the volcano. Since then, slow growth of the lava dome has occurred and as of August 2, the last clear view of the summit, the lava dome was about 50 meters (164 feet) in diameter. Thermal anomalies were detected in satellite images intermittently throughout the week when cloud cover was limited or absent.

The formation of a lava dome is consistent with observed thermal anomalies seen since July 19, 2011 indicating that the dome probably has been growing since that time. The persistent but generally weak thermal anomalies may be indicative of a slow growing or cooling lava dome. The presence of a lava dome increases the possibility of an explosive, ash-producing eruption, but does not necessarily mean that explosive activity will occur over the coming days to weeks. Short-lived explosions from the summit vent have occurred during previous periods of unrest at Cleveland volcano, and such events can produce ash clouds that exceed 20,000 feet above sea level. Explosive events can occur without warning and ash clouds may go undetected in satellite imagery for hours.

Without a real-time seismic network on the volcano, AVO is unable to track local earthquake activity related to volcanic unrest, provide forecasts of eruptive activity, or confirmation of explosive, ash-producing events. AVO is monitoring the volcano using satellite data as it becomes available.

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.

VOLCANO ALERT LEVELS

NORMALVolcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

ADVISORYVolcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

WATCHVolcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway but poses limited hazards.

WARNINGHazardous eruption is imminent, underway, or suspected.

AVIATION COLOR CODES

GREENVolcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

YELLOWVolcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

ORANGEVolcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway with no or minor volcanic-ash emissions [ash-plume height specified, if possible].

REDEruption is imminent with significant emission of volcanic ash into the atmosphere likely OR eruption is underway or suspected with significant emission of volcanic ash into the atmosphere [ash-plume height specified, if possible].